[Mathematica]Plotting 3D line with data point

I can use the Show function to combine multiple plots, so I know how to plot data points and a calculated fit line in 2D, but now I want to do the same in 3 dimensions. I can plot the data points just fine in 3D, but I don't know how to draw a straight line with a know equation in 3D.
My equation is of the form z=beta0 + beta1 x + beta2 y, and Plot3D just gives a blank output with that equation as input (I think because it expects to plot a surface a not a line). Thanks in advanced for any help!